JP2015216084A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a start method of a fuel cell system which raises the temperature along a cathode passage as equally as possible.SOLUTION: Start method of a fuel cell system includes a warming necessity determination step for determining the necessity of warming of a stack, a normal power generation step for supplying refrigerant at a predetermined normal power generation refrigerant flow rate to the stack and supplying air at a predetermined normal power generation air flow rate when a determination is made that warming is unnecessary, and reaction gas reduction step (time t0-t1) for supplying refrigerant at a reduction time refrigerant flow rate lower than the normal power generation refrigerant flow rate to the stack when warming is necessary and a determination is made that a request power generation current value for the fuel cell is equal to or lower than a predetermined threshold, and supplying air at a reduction time air flow rate lower than the normal power generation air flow rate to the stack.

Description

  The present invention relates to a fuel cell system.

  BACKGROUND ART A fuel cell system that generates electric power using an electrochemical reaction of a reaction gas in a fuel cell includes a refrigerant circulation device that circulates a refrigerant in order to control the temperature of the fuel cell during power generation. In addition, if the cooled refrigerant is circulated, the temperature of the entire fuel cell may decrease. Therefore, when the fuel cell system is started at a low temperature, the water generated during power generation freezes inside the fuel cell. In order to prevent this, the circulation of the refrigerant is often stopped (see, for example, Patent Document 1).

JP 2003-36874 A

  By the way, in the fuel cell, the power generation reaction does not always proceed uniformly in all planes where the reaction gas flows. In particular, immediately after the start of the fuel cell, the water content of the membrane electrode structure constituting the fuel cell tends to vary, and the variation tends to occur between the portion where the power generation reaction proceeds easily and the portion where it is difficult to proceed.

  Further, since the water generated by the power generation flows along the flow path of the reaction gas, the membrane electrode structure immediately after the activation becomes wet from the vicinity of the outlet side of the flow path of the reaction gas. For this reason, immediately after activation, the power generation reaction tends to proceed more easily on the outlet side than on the inlet side in the flow path of the reaction gas. On the other hand, when the circulation of the refrigerant is stopped at the time of low temperature startup of the fuel cell system as in the above-mentioned Patent Document 1, although the temperature decrease of the entire fuel cell can be prevented, the variation in the temperature distribution inside the fuel cell tends to increase. . For this reason, if the circulation of the refrigerant is stopped immediately after startup, the temperature difference between the inlet side and the outlet side of the reaction gas in the inside of the fuel cell becomes more conspicuous, and as a result, on the outlet side than the inlet side of the fuel cell. A phenomenon that power generation is concentrated may occur.

  An object of the present invention is to provide a method for starting a fuel cell system that raises the temperature as much as possible along the flow path of the reaction gas.

  (1) A fuel cell system (for example, a fuel cell system 1 described later) includes a fuel cell (for example, a fuel cell stack 2 described later) that generates power when a reaction gas (for example, oxygen and hydrogen described later) is supplied; A reaction gas supply device (for example, an air compressor 41, an EGR pump 46, a hydrogen tank 31, and an injector 35, which will be described later) for supplying a reaction gas to the fuel cell, and a refrigerant supply device (for example, a refrigerant supply device for supplying refrigerant to the fuel cell) And a water pump 52) to be described later. The start-up method of the fuel cell system according to the present invention does not require a warm-up necessity determination step (for example, a process of S1 in FIG. 2 described later) for determining whether or not the fuel cell needs to be warmed up. Is determined, the refrigerant is supplied to the fuel cell at a predetermined normal refrigerant flow rate (for example, a normal power generation refrigerant flow rate in FIG. 3 described later), and the reaction gas is supplied to a predetermined normal power generation flow rate (for example, described later). If it is determined that the normal power generation step (for example, the process of S4 in FIG. 2 described later) and warm-up are required, the refrigerant is supplied. A refrigerant flow rate reduction step (for example, an air flow rate reduction process of S12 in FIG. 4 described later) and a refrigerant flow rate reduction process for supplying the fuel cell with a warm-up refrigerant flow rate (for example, a reduced refrigerant flow rate in FIG. 3 described later) smaller than the normal refrigerant flow rate. Normal warm-up process of S13) and the fuel cell The required current generation value to be acquired, and a required current determination step (for example, the process of S25 in FIG. 5 described later) for determining whether or not the required generated current value is equal to or less than a predetermined threshold value are required. When it is determined that the required power generation current value is equal to or less than the threshold value, the warm-up power generation flow rate (for example, the reduced air flow rate of FIG. And a reactive gas reduction step (for example, an air flow rate reduction process in S12 of FIG. 4 described later) supplied to the fuel cell at a warm-up power generation concentration lower than the normal power generation concentration.

  (2) In this case, it is preferable not to perform the reactive gas reduction step when it is determined that the required power generation current value is larger than the threshold value.

  (3) In this case, the start-up method acquires the temperature on the inlet side of the flow path of the reaction gas inside the fuel cell, and determines whether the temperature on the inlet side is equal to or higher than a predetermined first temperature. When it is determined that the temperature on the inlet side is equal to or higher than the first temperature while performing the inlet temperature determination step (for example, the process of S22 in FIG. 5 described later) and the reactive gas reduction step. Is a reaction gas return step (for example, the processing of S23 in FIG. 5 described later) for increasing the flow rate of the reaction gas above the warm-up power generation flow rate or increasing the concentration of the reaction gas above the warm-up power generation concentration. Are preferably further provided.

  (4) In this case, the start-up method obtains the maximum temperature inside the fuel cell and determines whether or not the maximum temperature is equal to or higher than a predetermined second temperature (for example, described later) If it is determined that the maximum temperature is equal to or higher than the second temperature during the process of S60 in FIG. 9 and the refrigerant flow rate reduction step, the flow rate of the refrigerant is set higher than the warm-up refrigerant flow rate. It is preferable to further include a refrigerant flow rate return step (for example, a process of S53 in FIG.

  (5) In this case, the start-up method further includes a moisture content acquisition step (for example, the process of S71 in FIG. 11 described later) for acquiring the moisture content of the membrane of the fuel cell, and requires warm-up, When it is determined that the required power generation current value is equal to or less than the threshold value and the moisture content is equal to or less than a predetermined value (for example, the determination in S72 of FIG. 11 described later is YES), the reactive gas reduction step. It is preferable to carry out.

  (1) In the present invention, whether or not warm-up is necessary is determined. When it is determined that warm-up is not necessary, the normal power generation process is performed, and when it is determined that warm-up is necessary, the refrigerant flow rate is determined. A reduction process and a reaction gas reduction process are performed. Particularly in the present invention, in the reaction gas reduction step, the flow rate or concentration of the reaction gas is reduced more than the flow rate or concentration in the normal power generation step. Then, in the fuel cell, the power generation reaction proceeds more easily on the inlet side than on the outlet side along the flow path of the reaction gas, so that it is possible to prevent power generation from concentrating on the outlet side as described above. Therefore, according to the present invention, the temperature can be increased evenly from the inlet side to the outlet side even in an environment where the flow rate of the refrigerant is reduced and the temperature distribution tends to vary. In addition, this makes it possible to warm up while suppressing variations in power generation performance of the fuel cell. Further, in the present invention, when the warm-up is necessary and the required power generation current value for the fuel cell is determined to be smaller than the predetermined threshold value, the reactive gas reduction step having the above-described effect is performed, so that the merchantability is improved. There is no loss. That is, it is possible to prevent the fuel cell from generating power according to the demand because the reactive gas reduction process is performed with priority given to warm-up.

  (2) Although the power generation reaction proceeding inside the fuel cell tends to be biased toward the outlet side as described above when the power generation current of the fuel cell is relatively small, the power generation current of the fuel cell is relatively large There is a tendency that the power generation reaction proceeds evenly from the entrance side to the exit side. That is, when the power generation current of the fuel cell is relatively large, it is less necessary to perform the reaction gas reduction step than when it is small. In addition, reducing the reaction gas increases the internal resistance of the fuel cell and increases the amount of heat generated by power generation, which is advantageous for warming up, but it is not possible to generate power as required as described above. The fuel cell is likely to deteriorate. Therefore, in the present invention, the reactive gas reduction process is performed only when the required power generation current value is equal to or less than the predetermined threshold value, and the reactive gas reduction process is not performed when the required power generation current value is larger than the threshold value. As a result, when the required power generation current value is large, priority can be given to outputting a current having a required magnitude, so that merchantability can be improved. Moreover, the deterioration of the fuel cell can be suppressed as much as possible by performing the reactive gas reduction step only when necessary.

  (3) As described above, power generation tends to concentrate on the reaction gas outlet side immediately after startup, whereas when the reaction gas reduction step is performed, power generation is concentrated on the reaction gas inlet side, and the temperature on the inlet side Can be raised. However, if power generation is concentrated on the inlet side, the temperature on the inlet side increases excessively and the membrane may be damaged. On the other hand, in the present invention, when the temperature on the inlet side exceeds the first temperature by performing the reaction gas reduction step, the flow rate or concentration of the reaction gas is increased to shift to power generation in the entire area. The state where power generation concentrates only on the inlet side can be eliminated, and damage to the membrane due to excessive temperature rise on the inlet side can be suppressed.

  (4) When the flow rate of the refrigerant is reduced as described above, the temperature of the entire fuel cell can be prevented from lowering, but the variation in temperature distribution inside the fuel cell tends to increase. In contrast, in the present invention, when the maximum temperature inside the fuel cell exceeds the second temperature during the refrigerant flow rate reduction step, the flow rate of the refrigerant is increased. As a result, the temperature of the entire fuel cell can be raised while the variation in temperature distribution is smoothed.

  (5) If the water content of the fuel cell membrane is sufficient to be suitable for power generation, the power generation reaction will not be biased toward the outlet side without reducing the flow rate and concentration of the reaction gas. Therefore, in the present invention, the reaction gas reduction step is performed when it is determined that warm-up is necessary, the required generated current value is equal to or less than the threshold value, and the moisture content of the membrane is equal to or less than the predetermined value. In this way, by performing the reactive gas reduction process only when necessary, deterioration of the fuel cell can be suppressed as much as possible while improving merchantability.

1 is a diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention. It is a flowchart which shows the specific procedure of the starting process of a fuel cell system. It is a figure which shows an example of the map which determines an air flow rate and a refrigerant | coolant flow rate. It is a main flowchart of a warm-up process. It is a flowchart which shows the procedure which updates a flag. It is a figure which shows the change of the entrance side temperature and exit side temperature of a stack during execution of warming-up process. It is a figure which shows the temperature distribution inside a stack. It is a figure which shows the temperature distribution inside a stack. It is a flowchart which shows the procedure which updates the flag in the fuel cell system which concerns on 2nd Embodiment of this invention. It is the modification 1 of the flowchart of FIG. It is the modification 2 of the flowchart of FIG.

<First Embodiment>
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a fuel cell system 1 according to the present embodiment.
The fuel cell system 1 includes a fuel cell stack 2, an anode system 3 that supplies hydrogen as a reaction gas to the fuel cell stack 2, and a cathode system 4 that supplies air containing oxygen as a reaction gas to the fuel cell stack 2. A diluter 37 that performs post-treatment of the gas discharged from the fuel cell stack 2, a cooling device 5 that cools the fuel cell stack 2, a battery B that stores electric power generated by the fuel cell stack 2, and a fuel cell stack 2 and a running motor M that drives tires (not shown) by supplying electric power from the battery B, and an ECU 6 that is an electronic control unit thereof. The fuel cell system 1 is mounted on a fuel cell vehicle (not shown) using the tire as a driving wheel.

  The fuel cell stack (hereinafter simply referred to as “stack”) 2 has a stack structure in which, for example, several tens to several hundreds of cells are stacked. Each fuel cell is configured by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure is composed of two electrodes, an anode electrode (cathode) and a cathode electrode (anode), and a solid polymer electrolyte membrane sandwiched between these electrodes. Usually, both electrodes are formed of a catalyst layer that performs an oxidation / reduction reaction in contact with the solid polymer electrolyte membrane and a gas diffusion layer in contact with the catalyst layer. In the stack 2, when hydrogen is supplied to the anode flow path 21 formed on the anode electrode side and oxygen-containing air is supplied to the cathode flow path 22 formed on the cathode electrode side, these electrochemical reactions occur. To generate electricity.

  The output current taken out from the stack 2 during power generation is input to the battery B and the load (travel motor M, air compressor 41, etc.) via the current controller 29. The ECU 6 calculates a required generated current value corresponding to a required value for the output current of the stack 2 based on an output signal from an accelerator opening sensor (not shown) that detects the opening of the accelerator pedal. The current controller 29 controls the output current of the stack 2 during power generation using the required power generation current value calculated by the ECU 6.

  The battery B stores electric power generated by the stack 2 and electric energy recovered as a regenerative braking force by the traveling motor M. Further, for example, when the fuel cell system 1 is started up or when the vehicle is operated at a high load, the electric power stored in the battery B is supplied to the load so as to supplement the output of the stack 2.

  The anode system 3 includes a hydrogen tank 31 that stores hydrogen gas at a high pressure, a hydrogen supply pipe 32 that extends from the hydrogen tank 31 to the introduction part of the anode flow path 21 of the stack 2, and a diluter 37 from the discharge part of the anode flow path 21. And a hydrogen reflux pipe 34 that branches from the hydrogen discharge pipe 33 and reaches the hydrogen supply pipe 32. The hydrogen circulation flow path for the gas containing hydrogen is constituted by a hydrogen supply pipe 32, an anode flow path 21, a hydrogen discharge pipe 33 and a hydrogen reflux pipe 34.

  In the hydrogen supply pipe 32, a main stop valve 312 and an injector for injecting new hydrogen gas supplied via the main stop valve 312 toward the stack 2 in this order from the hydrogen tank 31 side to the stack 2 side. 35 is provided. The flow rate of hydrogen supplied to the anode passage 21 of the stack 2 during power generation and the pressure in the anode passage 21 are controlled by opening and closing the injector 35.

  A purge valve 33 a is provided in the hydrogen discharge pipe 33 on the downstream side of the connection portion with the hydrogen reflux pipe 34. When the hydrogen concentration of the gas circulating in the hydrogen circulation channel decreases, the power generation efficiency of the stack 2 decreases. For this reason, the purge valve 33a is opened at an appropriate timing during the power generation of the stack 2. Thereby, the gas in the hydrogen circulation channel is discharged to the diluter 37.

  The cathode system 4 includes an air compressor 41, an air supply pipe 42 extending from the air compressor 41 to the introduction part of the cathode flow path 22, an air discharge pipe 43 extending from the discharge part of the cathode flow path 22 to the diluter 37, and an air discharge An air reflux pipe 45 branched from the pipe 43 to the air supply pipe 42 and a stack bypass pipe 48 branched from the air discharge pipe 43 to the hydrogen supply pipe 32 and the diluter 37 are configured. The oxygen circulation flow path of the gas containing oxygen is constituted by the air supply pipe 42, the cathode flow path 22, the air discharge pipe 43 and the air reflux pipe 45.

  The air compressor 41 supplies air outside the system to the cathode flow path 22 of the stack 2 via the air supply pipe 42. The air exhaust pipe 43 is provided with a back pressure valve 43b for adjusting the pressure in the cathode flow path 22. The flow rate of air supplied to the cathode flow path 22 of the stack 2 during power generation (hereinafter referred to as “air flow rate”) is controlled by adjusting the rotational speed of the air compressor 41.

  The air reflux pipe 45 is provided with an EGR pump 46 that pumps the gas on the air discharge pipe 43 side to the air supply pipe 42 and circulates the oxygen-containing gas in the oxygen circulation passage. When the EGR pump 46 is driven, a part of the gas discharged from the outlet side of the cathode channel 22 of the stack 2 is returned to the inlet side of the cathode channel 22. Therefore, by continuing to drive the EGR pump 46, the ratio of the amount of gas recirculated through the air recirculation pipe 45 to the amount of air newly supplied from the air compressor 41 can be increased. The oxygen concentration of the gas in the cathode flow path 22 can be reduced.

  The stack bypass pipe 48 is provided with a bypass valve 48 a that controls the flow rate of air flowing from the air compressor 41 to the diluter 37, and a scavenging valve 48 b that controls the flow rate of air flowing from the air compressor 41 to the hydrogen supply pipe 32. It has been. The bypass valve 48 a is opened when, for example, the back pressure valve 43 b is closed and dilution gas cannot be supplied from the air discharge pipe 43 to the diluter 37, and supplies air immediately below the air compressor 41 to the diluter 37. The scavenging valve 48b performs a scavenging process in which impurities remaining in the hydrogen circulation flow path are discharged with air supplied from the air compressor 41 while power generation by the stack 2 is stopped, or the anode flow path of the stack 2 Opened to reduce the hydrogen concentration in the 21.

  The diluter 37 uses the gas introduced through the back pressure valve 43b and the bypass valve 48a as a dilution gas, dilutes the gas containing hydrogen discharged through the purge valve 33a, and discharges it out of the system. .

  The cooling device 5 includes a refrigerant circulation channel 51 including the stack 2 as a path, a water pump 52 that pumps the refrigerant in the refrigerant circulation channel 51 in a predetermined direction, and a radiator 53 that is a part of the refrigerant circulation channel 51. And a radiator fan 54 that cools the refrigerant flowing through the radiator 53. The flow rate of the refrigerant supplied to the stack 2 (hereinafter referred to as “refrigerant flow rate”) is controlled to a size suitable for the power generation state of the stack 2 by adjusting the rotational speed of the water pump 52.

  Sensors such as a current sensor 27, a stack temperature sensor 28, and a cell voltage sensor 26 are connected to the ECU 6 in order to grasp the power generation state of the stack 2. The current sensor 27 detects the output current of the stack 2 and outputs a signal substantially proportional to the detected value to the ECU 6. The stack temperature sensor 28 detects the temperature at a predetermined portion of the stack 2 and outputs a signal substantially proportional to the detected value to the ECU 6. The cell voltage sensor 26 detects a cell voltage generated in the fuel cells constituting the stack 2 and outputs a signal substantially proportional to the detected value to the ECU 6.

  An ignition switch IG that can be operated by the driver is provided in a driver's seat of a vehicle (not shown). The ignition switch IG outputs a start command signal for the fuel cell system 1 to the ECU 6 when turned on by the driver, and outputs a stop command signal for the fuel cell system 1 to the ECU 6 when turned off from the on state. .

  FIG. 2 is a flowchart showing a specific procedure of the starting process of the fuel cell system. This activation process is executed by the ECU in response to detection of an activation command signal from the ignition switch.

  First, in S1, the ECU determines whether or not the fuel cell system needs to be warmed up. More specifically, the ECU determines whether the stack temperature acquired based on the output of the temperature sensor is equal to or lower than a predetermined warm-up determination temperature, or until the ignition switch is turned on this time after the ignition switch is turned off last time. When the time (so-called soak time) is equal to or longer than a predetermined warm-up determination time, it is determined that it is necessary to execute the warm-up process of the fuel cell system. Otherwise, the warm-up time of the fuel cell system is determined. It is determined that it is not necessary to execute the machine process.

  If the determination in S1 is NO, the ECU immediately starts normal power generation without executing the warm-up process in S2 (S4). In this normal power generation, the ECU controls the air flow rate and the refrigerant flow rate based on a predetermined input using, for example, a map as shown by a solid line in FIG. If the determination in S1 is YES, the ECU executes the warm-up process described with reference to FIGS. 4 to 8 until it is determined in S3 that the warm-up of the fuel cell system has been completed. The ECU determines that the warm-up of the fuel cell system has ended when a warm-up end flag Ffin described later is 1. The warm-up end flag Ffin is a flag indicating that the warm-up process in S2 has been completed, and is updated by a flag update process in FIG. The warm-up completion flag Ffin is set to 0 immediately after turning on the ignition switch. In the following, the air flow rate determined using the map shown by the solid line in FIG. 3 is referred to as a normal power generation air flow rate, and the refrigerant flow rate is referred to as a normal power generation refrigerant flow rate.

  FIG. 4 is a main flowchart of the warm-up process. This process is repeatedly executed by the ECU until it is determined in S3 of FIG. 2 that the warm-up of the fuel cell system has been completed.

  In S11, the ECU determines whether or not the air reduction flag Fair is 1. This air reduction flag Fair is a flag indicating that execution of an air flow rate reduction process, which will be described later, is requested so that power generation is performed more preferentially on the inlet side than on the outlet side of the cathode flow path of the stack. It is. This flag Fair is updated by a flag update process of FIG. 5 described later. The flag Fair is set to 1 immediately after turning on the ignition switch.

  When determination of S11 is YES, it moves to S12. In S12, the ECU controls the air flow rate and the refrigerant flow rate using a map as shown by a one-dot chain line in FIG. In the following, the air flow rate determined using the map shown by the one-dot chain line in FIG. 3 is referred to as a reduced air flow rate, and the refrigerant flow rate is referred to as a reduced refrigerant flow rate. As shown in FIG. 3, the reduced air flow rate and the reduced refrigerant flow rate are determined to be smaller than the normal power generation air flow rate and the normal power generation refrigerant flow rate, respectively. Hereinafter, supplying the refrigerant having the reduced refrigerant flow while supplying the air having the reduced air flow is referred to as air flow reduction processing.

  Here, the effect of the air flow rate reduction process in S12 will be described. As described above, when the air flow rate is reduced, the internal resistance of the stack increases, so that the temperature rise of the stack increases. Further, as described above, the power generation reaction tends to be biased toward the outlet side of the cathode flow channel within the stack immediately after startup. On the other hand, when the air flow rate is further reduced from the above-described normal power generation air flow rate, the power generation reaction inside the stack is preferentially advanced on the inlet side of the cathode flow path having a higher oxygen concentration. In the air flow rate reduction process of S12, by reducing the air flow rate to the reduced air flow rate, the power generation reaction can be advanced on the inlet side, and the temperature on the inlet side can be quickly raised. Further, when the refrigerant is circulated, the temperature distribution of the entire stack tends to decrease, although the variation in the temperature distribution inside the stack is reduced. In the air flow rate reduction process of S12, the temperature increase effect on the inlet side by reducing the air flow rate as described above can be prevented from being prevented by reducing the refrigerant flow rate to the refrigerant flow rate at the time of reduction.

  When determination of S11 is NO, it moves to S13. In S13, the ECU controls the air flow rate using a map as shown by a solid line in FIG. 3, and controls the refrigerant flow rate using a map as shown by a one-dot chain line in FIG. That is, in S13, the ECU increases the air flow rate to the normal power generation air flow rate while reducing the refrigerant flow rate to the reduced refrigerant flow rate. Hereinafter, supplying the refrigerant with the reduced refrigerant flow rate while supplying the air with the normal power generation air flow rate will be referred to as the normal warm-up process.

  Here, the effect of the normal warm-up process in S13 will be described. When the air flow rate reduction process described above is executed, the generated water tends to accumulate in the cathode flow path of the stack due to the reduction of the air flow rate. The normal warm-up process in S13 increases the air flow rate to the normal power generation air flow rate while reducing the flow rate of the refrigerant, thereby suppressing the temperature drop of the stack due to the circulation of the cooled refrigerant, It can be discharged from the stack. Moreover, since the oxygen concentration on the outlet side increases, the power generation using the entire region is shifted.

  FIG. 5 is a flowchart showing a procedure for updating the warm-up end flag Ffin and the air reduction flag Fair referred to in the processes of FIGS. 2 and 4. In other words, FIG. 5 is a flowchart showing the procedure for selecting whether or not to execute the warm-up process of FIG. 4 and either the normal warm-up process or the air flow rate reduction process of FIG. The flag update process of FIG. 5 is repeatedly executed by the ECU until it is determined in S3 of FIG. 2 that the warm-up of the fuel cell system has been completed, similarly to the warm-up process of FIG.

  In S21, the ECU acquires the average temperature of the stack based on the output of the temperature sensor, and determines whether or not this average temperature exceeds a predetermined warm-up end determination temperature. If the determination in S21 is YES, the process proceeds to S23, and the warm-up end flag Ffin is changed from 0 to 1. As a result, the warm-up process ends, and the process shifts to normal power generation (see FIG. 2). If the determination in S21 is no, the process proceeds to S22.

  In S22, the ECU acquires the inlet temperature of the cathode flow path of the stack and determines whether or not the inlet temperature is equal to or higher than a predetermined first temperature. As described above, when the air flow rate reduction process or the refrigerant flow rate reduction process is executed, power generation is concentrated on the inlet side of the cathode flow path inside the stack, and the temperature on the inlet side rises. Therefore, the timing of completing the air flow rate reduction process or the refrigerant flow rate reduction process and shifting to the normal warm-up process can be determined by the stack inlet temperature. The stack inlet temperature can be estimated based on the output of the stack temperature sensor, the integrated value of the generated current of the stack, and the time when the air flow rate reduction process and the refrigerant flow rate reduction process are executed. Further, when an inlet temperature sensor for detecting the temperature on the inlet side of the cathode flow path of the stack is provided, the inlet temperature may be calculated using the output of this sensor.

  If the determination in S22 is YES and the inlet temperature rises to the first temperature, the process proceeds to S23. In S23, the ECU changes the warm-up end flag Ffin from 0 to 1 to end the warm-up process (see S23). As a result, the warm-up process ends, and the process shifts to normal power generation (see S3 in FIG. 2). In other words, when the air flow rate reduction processing has been performed so far (when Fair = 1), the ECU normally reduces the air flow rate from the reduced air flow rate according to the fact that the inlet temperature has exceeded the first temperature. Increase to the power generation air flow rate.

  If the determination in S22 is no, the process proceeds to S24. In S24, the ECU acquires the cell voltage value of the stack based on the output of the cell voltage sensor, and determines whether or not the cell voltage value is equal to or less than a predetermined threshold value. When the air flow rate reduction process is executed as described above, the air flow rate is reduced to the reduced air flow rate, so that water generated by the power generation reaction tends to accumulate in the cathode flow path. In addition, when the generated water is excessively accumulated in the cathode channel, the cell voltage tends to decrease. If the determination in S24 is NO, the process proceeds to S25, and if the determination is YES, the process proceeds to S28.

  In S25, the ECU calculates a required power generation current value and determines whether or not this required current value is equal to or less than a predetermined threshold value. When the power generation current of the stack is large, the power generation reaction in the stack tends to progress evenly from the inlet side to the outlet side without being biased toward the outlet side of the cathode flow path. poor. Therefore, if the determination in S25 is NO, the ECU sets the air reduction flag Fair to 0 in order to increase the air flow rate to the normal power generation air flow rate (see S26). Accordingly, as described with reference to FIG. 4, the normal warm-up process is executed in which only the refrigerant flow rate is reduced to the reduced refrigerant flow rate and the air flow rate is increased to the normal warm-up air flow rate (S <b> 13 in FIG. 4). reference).

  On the other hand, when the power generation current of the stack is small, the power generation reaction in the stack tends to be biased toward the outlet side of the cathode flow path. Therefore, when the air flow rate is reduced so that the power generation reaction proceeds preferentially on the inlet side. It is preferable to reduce the flow rate. Therefore, if the determination in S25 is YES, the ECU sets the air reduction flag Fair to 1 to reduce the air flow rate and the refrigerant flow rate to the reduced air flow rate and the reduced refrigerant flow rate. Thereby, as described with reference to FIG. 4, the air flow rate reduction process is executed (see S12 of FIG. 4).

  Returning to the processing of S24, the case where the cell voltage value has decreased to a threshold value or less will be described. If the determination in S24 is YES, the process moves to S28. In S28, the ECU determines whether or not a predetermined time has elapsed since the decrease in the cell voltage was confirmed for the first time in the process of S24. If the determination in S28 is NO, the process moves to S26, and the air reduction flag Fair is set to 0 as described above. As a result, the air flow rate is normally increased to the warm-up air flow rate, so that the discharge of the generated water accumulated in the cathode flow channel is promoted and the cell voltage is expected to recover.

  If the determination in S28 is YES, that is, if the cell voltage does not recover even after a predetermined time has elapsed since the air flow rate was increased as described above, the process proceeds to S29. In S29, the ECU starts a process (not shown) for recovering the cell voltage by further increasing the air flow rate or limiting the output current, and moves to S23 to end the warm-up process. .

Next, the effect of the warm-up process as described above will be described with reference to FIGS.
FIG. 6 is a diagram illustrating changes in the inlet side temperature and the outlet side temperature of the stack during execution of the warm-up process. In FIG. 6, two thick solid lines and thick broken lines indicate changes in the temperature on the inlet side and the outlet side of the stack when the warm-up process (FIGS. 4 and 5) according to the present embodiment is performed. Also, two thin solid lines and thin broken lines indicate changes in the temperatures on the inlet side and the outlet side of the stack when only the normal warm-up process of S12 in FIG. 4 is performed, respectively.

  In FIG. 6, warm-up processing is started in response to the ignition switch being turned on at time t0, air flow reduction processing (see S12 in FIG. 4) is performed from time t0 to time t1, and time t1 to time t2 The normal warm-up process (see S13 in FIG. 4) is executed until the normal power generation is performed.

  FIG. 7 is a diagram showing the temperature distribution inside the stack at times t1 and t3 when only the normal warm-up process is performed. FIG. 8 is a diagram showing the temperature distribution inside the stack at times t1, t2, and t3 when the warm-up process according to the present embodiment is performed. 7 and 8, the cathode channel inlet side is the upper side, and the cathode channel outlet side is the lower side.

  When the process of reducing the air flow rate or the refrigerant flow rate is not performed, the power generation reaction tends to concentrate on the outlet side. For this reason, as shown by a thin solid line and a thin broken line in FIG. 6, the temperature on the outlet side rises quickly, whereas the temperature rise on the inlet side is moderate. As a result, as shown in FIG. 7, even when the warm-up process is executed from time t0 to t3, the variation in temperature distribution remains large, and the temperature on the inlet side does not increase so much.

  On the other hand, in the present embodiment, since the power generation reaction proceeds mainly on the inlet side by reducing the air flow rate and the refrigerant flow rate from the time t0 to the time t1, the temperature rise on the outlet side slows down, but the inlet side The temperature rises significantly. Thereafter, from time t1 to t2, when the air flow rate is increased while reducing only the refrigerant flow rate, the temperature on the inlet side rises, stops and gradually decreases, but power generation on the outlet side is promoted, and the temperature on the outlet side increases. start. Thereafter, when both the air flow rate and the refrigerant flow rate are increased from time t2 to t3, the temperature inside the stack rises as a whole while the variation in temperature distribution becomes gentle. As a result, both the inlet side and the outlet side can be raised to an appropriate temperature.

Second Embodiment
Next, a second embodiment of the present invention will be described with reference to the drawings. In the following, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The second embodiment differs from the above-described first embodiment in the procedure of the warm-up process flag update process executed by the ECU.

  FIG. 9 is a flowchart showing a specific procedure of flag update processing according to the present embodiment. Note that the processing of S51 to S59 in the processing of FIG. 9 is the same as the processing of S21 to S29 of FIG.

  When determination of S52 is YES, it moves to S60. In S60, the ECU acquires the maximum stack temperature corresponding to the temperature of the highest temperature portion of the stack, and determines whether or not the maximum stack temperature is equal to or higher than the second temperature higher than the first temperature. . As described above, when the flow rate of the refrigerant is reduced, variation in the temperature distribution of the stack tends to increase. Therefore, when the maximum temperature of the stack exceeds the second temperature, it is preferable to increase both the air flow rate and the refrigerant flow rate to the normal power generation air flow rate and the normal power generation refrigerant flow rate so that the variation in the temperature distribution becomes gentle. Therefore, if the determination in S60 is YES, the ECU proceeds to S53 and sets the warm-up end flag Ffin to 1. As a result, the warm-up process ends, and the process shifts to normal power generation (see FIG. 2). If the determination in S60 is NO, the process proceeds to S56, and the process proceeds to S56 in order to increase only the air flow rate to the normal power generation air flow rate while reducing the refrigerant flow rate.

As mentioned above, although two embodiment of this invention was described, this invention is not limited to these.
For example, in the above embodiment, the case where the air flow rate is reduced stepwise so that power generation proceeds intensively on the inlet side of the cathode flow path of the stack 2 (see FIG. 3) has been described. Not limited to. For example, even if the oxygen concentration of the gas flowing into the cathode flow path 22 is reduced instead of reducing the air flow rate, power generation can be advanced intensively on the inlet side of the cathode flow path. Note that the oxygen concentration of the gas flowing into the cathode channel 22 can be reduced by driving the EGR pump 46 of FIG. That is, by driving the EGR pump 46 and increasing the ratio of the amount of gas recirculated through the air recirculation pipe 45 to the amount of fresh air supplied from the air compressor 41, the gas flowing into the cathode flow path 22 The oxygen concentration of can be reduced.

  Further, instead of reducing the air flow rate and the oxygen concentration as described above, if the gas flow rate and the hydrogen concentration flowing into the anode flow channel 21 are reduced, power generation is focused on the inlet side of the anode flow channel similarly. Can be advanced. The flow rate of the gas flowing into the anode channel 21 can be reduced using the injector 35 of FIG. Further, the hydrogen concentration of the gas flowing into the anode channel 21 can be reduced by using the purge valve 33a and the scavenging valve 48b of FIG. That is, the hydrogen concentration of the gas flowing into the anode channel 21 can be reduced by opening the purge valve 33a and extending the interval for discharging the gas flowing through the hydrogen circulation channel. Further, by opening the scavenging valve 48b and introducing the air from the air compressor 41 into the hydrogen supply pipe 32, the hydrogen concentration of the gas flowing into the anode passage 21 can be reduced.

  FIG. 10 is a first modification of the flowchart of FIG. In the processes of FIGS. 5 and 9 described above, when the state in which the cell voltage value is equal to or lower than the predetermined threshold value continues for a predetermined time during the warm-up process (S24 and S28 in FIG. 5 or FIG. 9 (see S54 and S58 in FIG. 9), the process for recovering the cell voltage is started and the warm-up process is ended (see S23 and S29 in FIG. 5 or S53 and S59 in FIG. 9), but the present invention is not limited to this. In addition, as shown in S61 of FIG. 10, when the cell voltage value greatly decreases in a short time, that is, when the decrease width of the cell voltage value in a predetermined time is larger than a predetermined threshold value, a process for recovering the cell voltage is performed. It may start and end the warm-up process.

FIG. 11 is a second modification of the flowchart of FIG. In the processing of FIG. 5 and FIG. 9 described above,
Although the necessity of reducing the air flow rate is determined based on the required output current value (see S25 in FIG. 5 or S55 in FIG. 9), the present invention is not limited to this. For example, when the membrane electrode structure of the stack 2 contains an amount of moisture suitable for power generation, the power generation reaction occurs at the outlet side of the cathode channel 22 without reducing the air flow rate to the reduced air flow rate. There is no concentration. Therefore, as shown in S71 and S72 of FIG. 11, the moisture content of the membrane electrode structure of the stack 2 is estimated, and the flag Fair is set to 0 to reduce the air flow rate only when the moisture content is not more than a predetermined value. You may make it change from 1 to 1. The moisture content of the membrane electrode structure can be estimated by measuring the impedance value of the stack 2 using an impedance measuring device (not shown).

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 2 ... Fuel cell stack 31 ... Hydrogen tank (reaction gas supply device)
35. Injector (reactive gas supply device)
41 ... Air compressor (reactive gas supply device)
46 ... EGR pump (reactive gas supply device)
52 ... Water pump (refrigerant supply device)

Claims (5)

A fuel cell system activation method comprising: a fuel cell that generates power when a reaction gas is supplied; a reaction gas supply device that supplies the reaction gas to the fuel cell; and a refrigerant supply device that supplies a refrigerant to the fuel cell. Because
A warm-up necessity determination step for determining whether the fuel cell needs to be warmed up;
A normal power generation step of supplying the refrigerant to the fuel cell at a predetermined normal refrigerant flow rate and supplying the reaction gas at a predetermined normal power generation flow rate or normal power generation concentration when it is determined that the warm-up is unnecessary; ,
When it is determined that warm-up is necessary, a refrigerant flow rate reducing step of supplying the refrigerant to the fuel cell at a warm-up refrigerant flow rate lower than the normal refrigerant flow rate;
A required current determination step for obtaining a required generated current value for the fuel cell and determining whether the required generated current value is a predetermined threshold value or less;
If it is determined that warm-up is necessary and the required power generation current value is less than or equal to the threshold value, the reaction gas is heated to a warm power generation flow rate lower than the normal power generation flow rate or lower than the normal power generation concentration. And a reactive gas reduction step of supplying the fuel cell with a mechanical power generation concentration.   2. The method of starting a fuel cell system according to claim 1, wherein the reactive gas reduction step is not performed when it is determined that the required power generation current value is larger than the threshold value. An inlet temperature determination step of acquiring the temperature on the inlet side of the flow path of the reaction gas inside the fuel cell and determining whether the temperature on the inlet side is equal to or higher than a predetermined first temperature;
When it is determined that the temperature on the inlet side is equal to or higher than the first temperature during the reaction gas reduction step, the flow rate of the reaction gas is increased from the warm-up power generation flow rate or the reaction The method of starting a fuel cell system according to claim 1, further comprising a reaction gas return step of increasing a gas concentration to be higher than the warm-up power generation concentration. A maximum temperature determination step of acquiring a maximum temperature inside the fuel cell and determining whether the maximum temperature is equal to or higher than a predetermined second temperature;
When it is determined that the maximum temperature is equal to or higher than the second temperature while the refrigerant flow rate reducing step is being performed, a refrigerant flow rate returning step for increasing the flow rate of the refrigerant beyond the warm-up refrigerant flow rate; The method of starting a fuel cell system according to any one of claims 1 to 3, further comprising: A water content acquisition step of acquiring the water content of the fuel cell membrane;
The reactive gas reduction step is performed when it is determined that warm-up is necessary, the required power generation current value is not more than the threshold value, and the moisture content is not more than a predetermined value. 5. The method for starting the fuel cell system according to any one of items 1 to 4.